Ceramic, circuit substrate and electronic circuit substrate by use thereof and process for producing ceramic

ABSTRACT

The present invention provides a ceramic having a first region comprising a dielectric porcelain having an insulating layer at the crystal grain boundary of a semiconductor porcelain containing 0.50 to 5.30 mol parts of MnO 2  and 0.02 to 0.40 mol parts of Y 2  O 3  per 100 mol parts of the principal components comprising 49.50 to 54.00 mol % of TiO 2  and 50.50 to 46.00 mol % of SrO, and a second region comprising a dielectric porcelain containing further 0.40 to 5.00 mol parts of Al 2  O 3  and 0.05 to 2.00 mol parts of SiO 2  per 100 mol parts of the principal components in addition to the composition of the first region, and also provides a circuit substrate and an electronic circuit substrate using the same ceramic.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a ceramic which can be utilized as theelectronic material such as dielectric porcelain substrate, etc. and acircuit substrate and an electronic circuit substrate by use of theceramic, and also a process for producing the ceramic.

2. Related Background Art

In the prior art, an electronic circuit substrate has been constitutedby providing only a conductor circuit, a conductor circuit and aresistance, or a conductor circuit, a resistance and a capacitor withinthe limited range, and other functional portions mounted as the deviceas separated from the substrate.

More specifically, for example, as a porcelain substrate of the priorart, a substrate primarily having a conductor and a resistor builttherein was used, and a capacitor was mounted by soldering thereon as achip member, etc. For this reason, miniaturization of electronic circuithas been limited. FIG. 1 shows an example thereof, in which 111 is aporcelain substrate, 112 a conductor circuit, 113 a resistor and 114 achip capacitor.

In recent years, attempts have been made to have a plurality ofcapacitors built in within a substrate by varying the dielectricconstants within the same porcelain substrate.

However, in the prior art, it has been very difficult to practice amethod for forming different dielectric portions within the samesubstrate. For example, as is self-explanatory when consideringcumbersomeness in preparing a laminated ceramic capacitor, a substratehaving a plurality of capacitors built therein has not yet been realizedor practically applied under the present situation. It has also been atechnical task to make portions with high dielectric constantssufficiently separated as the device functional portions to the extentthat no influence may be exerted on each other in actuation within thelimited structural space.

Further, such problem of building in separately the functional portionsconcerned with electronic parts or circuit substrates are not limited todielectric porcelains, but has revealed itself generally in the case offorming two or more of the same kind or different kinds of functionalportions within the ceramic.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a ceramic capableof building therein a plurality of functional portions sectionalized assufficiently separated from each other.

A second object of the present invention is to provide a circuitsubstrate and an electronic circuit substrate capable of buildingtherein a plurality of electronic part constituent units as sufficientlyseparated from each other as the device functional parts, by beingconstituted of a ceramic capable of building therein a plurality offunctional portions sectionalized as sufficiently separated from eachother as mentioned above.

The above first object can be accomplished by a ceramic, having a firstregion comprising a dielectric porcelain having an insulating layer atthe crystal grain boundary of a semiconductor porcelain containing 0.50to 5.30 mol parts of MnO₂ and 0.002 to 0.40 mol parts of Y₂ O₃ per 100mol parts of the principal components comprising 49.50 to 54.00 mol % ofTiO₂ and 50.50 to 46.00 mol % of SrO, and a second region comprising adielectric material porcelain containing further 0.40 to 5.00 mol partsAl₂ O₃ and 0.05 to 2.00 mol parts of SiO₂ in addition to the compositionof said first region.

The above first object can also be accomplished by a process forproducing a ceramic comprising the steps: feeding a mixture and/or acompound comprising 60 to 98 mol % of Al₂ O₃ and 40 to 20 mol % of SiO₂onto the surface of a molded product containing 0.05 to 5.30 mol partsof MnO₂ and 0.02 to 0.40 mol parts of Y₂ O₃ per 100 mol parts of themain components comprising 49.50 to 54.00 mol % of TiO₂ and 50.50 to46.00 mol % of SrO, and diffusing said compound into the inner portionof said molded product.

The above second object can be accomplished by a circuit substratehaving electrodes internally of or on the surface of a ceramic having afirst region comprising a dielectric porcelain having an insulatinglayer at the crystal grain boundary of a semiconductor porcelaincontaining 0.50 to 5.30 mol parts of MnO₂ and 0.02 to 0.40 mol parts ofY₂ O₃ per 100 mol parts of principal components comprising 49.50 to54.00 mol % of TiO₂ and 50.50 to 46.00 mol % of SrO, and a second regioncomprising a dielectric porcelain containing further 0.40 to 5.00 molparts of Al₂ O₃ and 0.05 to 2.00 mol parts of SiO₂ in addition to thecomposition of said first region, and an electronic circuit substratehaving electrodes internally of or on the surface of a ceramic having afirst region comprising a dielectric porcelain having an insulatinglayer at the crystal grain boundary of a semiconductor porcelaincontaining 0.05 to 5.30 mol parts of MnO₂ and 0.02 to 0.40 mol parts ofY₂ O₃ per 100 mol parts of principal components comprising 49.50 to54.00 mol % of TiO₂ and 50.50 to 46.00 mol % of SrO, and a second regioncomprising a dielectric porcelain containing further 0.40 to 5.00 molparts of Al₂ O₃ and 0.05 to 2.00 mol parts of SiO₂ in addition to thecomposition of said first region, and having an electronic circuit partmounted on said ceramic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of the porcelain substrate of theprior art.

FIG. 2 through FIG. 4 are schematic sectional views showing the shapeexamples of the first region and the second region of in the ceramic ofthe present invention, respectively.

FIG. 5 is a schematic perspective view of a mold for preparing theceramic of the present invention, FIGS. 6A and 6B are respectivelyschematic perspective views of the molded product coated with a paste ofe.g. alumina and the ceramic provided with electrodes, and FIG. 7 is adiagram for illustration of the steps for preparation of the ceramic.

FIG. 8A is a plan view showing the constitutional example of the ceramicof the present invention, and FIG. 8B is a cross-sectional view alongA--A in FIG. 8A.

FIG. 9 and FIG. 10 are each schematic sectional view showing aconstitutional example of the circuit substrate of the presentinvention, and FIG. 11 is a schematic sectional view showing aconstitutional example of the electronic circuit substrate of thepresent invention.

FIG. 12 is a schematic sectional view showing the method for measuringthe flexural strength of the ceramic molded product.

FIG. 13 and FIG. 14 are respectively graphs showing the changes inparticle size internally of the porcelain and dielectric constantrelative to the mixing ratio of Al₂ O₃ to SiO₂.

DETAILED DESCRIPTION OF THE INVENTION

When the ceramic of the present invention is utilized as, for example,electronic material ceramic, the above functional portion capable ofbeing built in within the ceramic of the present invention may include,for example, electronic part constituting units such as dielectricmaterial constituting condensor, conductor, semiconductor, resistor,insulator, diode, transistor, etc. In the present invention, thesefunctional portions can be formed in the above first region or thesecond region, and also can be formed in a combination of these regions,a combination of these regions with other regions than these, or even ina region other than these regions.

Also, for example, by arranging two or more of the above first regionsseparated from each other with the above second region interposedtherebetween, or contrariwise by arranging two or more of the abovesecond regions separated from each other with the above first regioninterposed therebetween, two or more functional regions constituted ofthe above first region or the second region can be formed as separatedsufficiently from each other. Also, both of the first region and thesecond region can be used as functional portions.

The second region according to the present invention can be utilized asa region with different characteristics by selecting freely therespective amounts of Al₂ O₃ and SiO₂ used and the ratio of these, andcan be utilized as various functional portions or regions for dividingthe functional portion as desired. Accordingly, by forming one or moreof the portion where Al₂ O₃ and SiO₂ exist within the ceramic, a desirednumber of the functional portions of one or two or more can besectionalized as sufficiently separated from each other.

When the ceramic of the present invention is utilized as, for example,electronic material ceramic, preferably the functional portion of thefirst region can be exemplified by electronic part constituting unitssuch as semiconductor, dielectric member for constituting capacitor,conductor, resistor, insulator, diode, transistor, etc. On the otherhand, as the second region when the functional portion of the firstregion is divided, it may preferably include, for example, an insulatorrelative to semiconductor, conductor, resistor, a lower dielectricrelative to higher dielectric for constituting a capacitor.

For example, when a region of dielectric constituting a capacitor as thefunctional portion is formed, the region in which Al₂ O₃ and SiO₂ existby diffusion, etc. according to the present invention can be utilized asthe region for separating the region of the dielectric constituting theabove capacitor.

As an example of the ceramic of the present invention, for theplate-shaped dielectric porcelain substrate, shape examples of theregion of the dielectric constituting the above capacitor (the firstregion) and the region with low dielectric constant formed by use of theportion where Al₂ O₃ and SiO₂ exist by diffusion, etc. (the secondregion) are shown in FIGS. 2 to 4. In the examples shown in FIGS. 2 to4, 1 is a plate-shaped dielectric material porcelain substrate, A thefirst region and B the second region.

In FIG. 2, the second region B with a rectangular cross-section reachingthe both main surfaces of the plate-shaped dielectric porcelainsubstrate are provided, and the two first regions A, A separated fromeach other are provided with the region B sandwiched therebetween.

In the example shown in FIG. 3, the two regions B, B with rectangularcross-sections are provided on the respective surface layers of the bothmain surfaces of the porcelain 1, and the two first regions A, Aseparated from each other are provided with these regions B, Bsandwiched therebetween.

In the example shown in FIG. 4, the second region B with a rectangularcross-section is provided on the surface layer portion of one mainsurface of the porcelain 1, and the two first regions separated fromeach other A, A are provided with the region B sandwiched therebetween.

In the examples shown in FIG. 2 to FIG. 4, one or two of the secondregion B are provided, but that is not limitative of the presentinvention, but the number can be determined depending on the desirednumber of the functional portions (first regions), and 3 or more regionscan be also provided, as a matter of course.

When the above first region is made the region of the dielectric forconstituting a capacitor, the first dielectric porcelain is required tohave high dielectric constant, and it is also desirable in combinationwith this requirement that the characteristics when constituting thedielectric material itself or a capacitor such as dielectric loss,temperature change rate of capacitance, etc. should be practicallypreferable.

In this case, the dielectric constant of the first dielectric porcelainshould be preferably 35,000 or higher. With such dielectric constant,even when the condition in shape of the ceramic may be taken intoaccount, a capacitor with a capacitance to the extent of about 0.047 uFcan be formed, and when applied to, for example, a video circuit, etc.,about half of the kinds of ceramic chip capacitors generally employedcan be formed within the ceramic.

When the first region is thus utilized as the higher dielectric region,the first dielectric porcelain should be preferably made to have adielectric constant of 10-fold or more of that of the second dielectricporcelain. This is a performance demanded for removing the influencemutually between the functional portions, and creation of a differencein dielectric constant of 10-fold or more will be very advantageous inminiaturization of the circuit.

When the above first region is made a higher dielectric material region,as the porcelain constituting the first region, a composition havingfirstly high dielectric constant, and having secondly good performancessuch as tan δ, temperature characteristics, etc. is preferred. As thematerial satisfying these requirements, semiconductor porcelains havinginsulated crystal grain boundaries have been known.

As the additive for insulating the crystal grain boundary, there can beused any conventionally known additive for forming an insulating layerat the crystal grain boundary of semiconductor porcelain. For example,there can be used oxides of iron, cobalt, bismuth, vanadium, chromium,lead, copper, etc., and particularly as preferably used in the presentinvention, bismuth oxide and sodium oxide.

In recent years, as the semiconductor porcelain of this kind, thosecontaining strontium titanate as the main component have been frequentlyused.

Here, the semiconductor porcelain comprising 0.5 to 5.3 mol parts ofMnO₂ and 0.02 to 0.40 mol parts of Y₂ O₃ added to 100 mol parts of themain components comprising 49.50 to 54.00 mol % of TiO₂ and 50.50 to46.00 mol % of Sro with its crystal grain boundary being insulated withBi₂ O₃, etc. has good dielectric characteristics as:

(1) dielectric constant=35000-14000;

(2) tanδ≦2%;

(3) the temperature change of dielectric constant within ±15% in thetemperature range of -25° C. to +85° C.

In the semiconductor porcelain, TiO₂ and SrO which are the maincomponents in the semiconductor porcelain can exist in the compositionas composite oxides such as solid solution, sole oxides respectively ofTiO₂ and SrO, or a mixture of these. The quantitative ratio of TiO₂ toSrO in the composition is made 49.50 to 54.00 mol % for TiO₂ and 50.50to 46.00 mol % for SrO, because if the amount of TiO₂ becomes too much,namely the amount of SrO is too small, the desired dielectric porcelainis lowered in dielectric constant, the temperature change of dielectricloss and dielectric constant become greater and yet the insulatingresistance of the porcelain is reduced. If the amount of TiO₂ becomessmaller, namely the amount of SrO becomes larger, the dielectricconstant of the desired dielectric material porcelain is lowered and thetemperature change of the dielectric constant becomes larger. Thequantitative ratio of TiO₂ to SrO in the composition of the presentinvention is determined for exhibiting optimally the desiredcharacteristics such as these dielectric constant, dielectric loss,temperature change of dielectric constant, insulating resistance ofporcelain, ability to be converted to semiconductor, etc. with goodbalance.

In the ceramic of the present invention, MnO₂ plays a role as thesintering aid for forming a porcelain, and its amount used is limited to0.50 mol parts or more per 100 mol parts of the above main componentscomprising TiO₂ and SrO, because if MnO₂ is less than 0.50 mol parts,the dielectric constant of the desired dielectric porcelain is loweredand also the temperature change of the dielectric constant becomesgreater. The amount was limited to 5.3 mol parts or lower per 100 molparts of the above main components comprising TiO₂ SrO, because if MnO₂exceeds 5.3 mol parts, the dielectric loss will be increased remarkably.

Next, in the ceramic of the present invention, Y₂ O₃ has the effect ofconverting the porcelain into a semiconductor, and its amount used islimited to 0.02 mol parts or more per 100 mol parts of the above maincomponents comprising TiO₂ and SrO, because if Y₂ O₃ is less than 0.02mol parts, the dielectric constant is lowered. The amount is limited to0.4 mol parts or less per 100 mol parts of the above main components ofTiO₂ and SrO, because if Y₂ O₃ exceeds 0.4 mol parts, the dielectricconstant is lowered and the dielectric loss becomes greater.

One specific feature of the present invention resides in making thesecond dielectric porcelain constituting the second region a porcelainwith different dielectric constant from the first region throughexistence of Al₂ O₃ and SiO₂.

For permitting the first and the second dielectric material porcelainsto exist in a ceramic as an integrated structure, they are required tohave reactivity at the boundary therebetween, and also it iscontrariwise desirable that the reactivity should not be too great sothat no deformation may occur at the bonded portion, the strengthdistribution may not be greatly changed, and the stress may not beincluded.

The present invention utilizes the property that the electricalcharacteristics of the porcelain can be changed greatly by the presenceof Al₂ O₃ and SiO₂, whereby it has been rendered possible to separatethe functional portions within a ceramic. For example, as described indetail in Reference examples shown below, when the amount of Al₂ O₃ andSiO₂ added is changed minutely, it was confirmed that the dielectricconstant was remarkably changed between the orders of some hundreds andsome ten thousands. Accordingly, without changing the compositions ofthe porcelains to great extent, they can be built within the sameceramic by sectionalizing areas with different dielectric constants.

An example of the method for preparing the ceramic of the presentinvention is described below. Here, the porcelain forming compositionfor constituting the semiconductor porcelain of the above first regionis called C₁ and the porcelain forming composition for constituting theabove second region is called C₂.

This preparation example can be conducted by the use of a mold as shownin FIG. 5.

More specifically, a detachable partitioning plate 12 is provided on amold 11 as shown in FIG. 5, C₁ is filled in 13, 14, and C₂ in 15,followed by removal of the partitioning plate. Then, pressure molding isperformed. Here, the both end portions are filled with composition C₁and the central portion is filled with composition C₂. In FIG. 6B, forexample, a was made equal to 3 mm, b=2 mm, c=3 mm, d=10 mm ande(thickness)=0.55 mm. The molded product is primarily fired to form asemiconductor, and subsequently coated with an additive which becomesthe diffused component on the surface of the semiconductor porcelainthus obtained, followed by secondary firing to form an insulating layerat the crystal grain boundary of the semiconductor porcelains, thusforming a dielectric porcelain.

One shape example of the ceramic of the present invention is shown inFIG. 8A (plan view), FIG. 8B (A--A cross-sectional view in FIG. 8A).

The ceramic shown in FIGS. 8A and 8B has a plurality of regions withhigher dielectric constant 71, 71, 71 . . . . formed as sectionalizedfrom each other internally of the plate-shaped dielectric porcelain 1,and these regions are mutually separated with the regions with lowerdielectric constant 72, 72, 72 . . . . .

Next, the circuit substrate of the present invention is characterized byhaving at least electrodes internally of or on the surface of theceramic of the present invention, and having, if desired, at least onefunctional portion of conductor, resistor and insulator, etc.

As a constitution example of the circuit substrate, when the sameelements are represented by the same symbols, the circuit substrateshown in FIG. 9 has a pair of electrode groups 81, 81a, 81, 81a, 81 81a,constituted of thick film electroconductive paste such as silver paste,etc. on both main surfaces of the respective regions with highdielectric constant on the ceramic shown in FIGS. 8A and 8B.

The example of circuit substrate shown in FIG. 10 is further providedwith the insulating layers 92, 92a with via hole portion 91 remainedoptionally by screen printing of an insulating material paste such asglass, etc., a conductor circuit portion 93 printed within the via hole91 and the insulating layer, and a resistor portion 94.

Further, the electronic circuit substrate of the present invention ischaracterized by having electrodes internally of or on the surface ofthe ceramic of the present invention, and having at least one functionalportion of conductor, resistor and insulator, etc. existed and anelectronic circuit part mounted on the ceramic, if necessary.

When the same element is represented by the same symbol, for example,the electronic circuit substrate shown in FIG. 11 has a flat package IC101 and a chip member 102 connected to the conductor circuit portion 93mounted thereon.

In the following, the present invention is described in more detail byreferring to Reference examples and Examples.

The respective starting materials of TiO₂, SrO, MnO₂ and Y₂ O₃ wereweighed so that the semiconductor porcelain with the compositionalratios shown in Table 1 could be obtained, and pulverized and mixed in awet system ball mill for 12 hours. The mixture after drying was addedwith a small amount of polyvinyl alcohol as the binder, granulated into24 to 80 mesh and molded into discs of 20 mm in diameter and 0.7 mm inthickness by hydraulic pressing. Next, the molded discs were calcined inthe air at 950° C. to burn the binder. The product was cooled to roomtemperature and fired in a reducing atmosphere comprising 10 vol. % ofhydrogen and 90 vol. % of nitrogen at 1400° C. for 4 hours.

The semiconductor porcelain thus obtained was soaked into a suspensioncomprising a weight ratio of ethyl alcohol:Bi₂ O₃ or Na₂ O=10:1, andthen fired in an oxidizing atmosphere at 1250° C. or 0.5 hours to forman insulating layer at the crystal grain boundary.

The discs of dielectric porcelains thus obtained (Sample Nos. 1-25) werecoated on both surfaces with silver paste, baked at 850° C. for 30minutes to form electrodes to prepare capacitors.

The dielectric constant (ε), the dielectric loss (tan δ), the insulatingresistance (IR) and the temperature characteristic of dielectricconstant (temperature changes at -25° C. and +85° C. with 25° C. as thestandard) of the dielectric porcelain constituting the capacitor thusobtained were measured to obtain the results shown in Table 1. Themeasurement conditions were 25° C. and a frequency of 1 kHz. Thesymbol * in Table 1 is a sample outside the scope of the presentinvention.

When Al₂ O₃ is added to the high dielectric constant composition(hereinafter called C₁), the porcelain crystal grain size is reduced andthe volume resistivity of the semiconductor porcelain increased withincrease of the amount of Al₂ O₃ added, with the result that thedielectric constant is markedly lowered upon being made into adielectric porcelaim.

In the present invention, SiO₂ added together with Al₂ O₃ hasparticularly the effect of improving the mechanical strength of thesecond region and the mechanical strength of the bonded interfacebetween the first region and the second region.

The effects of the addition of Al₂ O₃ and the addition of Al₂ O₃ andSiO₂ are exemplified in Table 2.

In C₁, when the amount of Al₂ O₃ added is less than 0.40 mol parts per100 mol parts of the main components (TiO 49.50 to 54.00 mol % and SnO50.50 to 46.00 mol %), the ratio of the dielectric constant lowered issmall, and the dielectric constant will be lowered to below 500 withaddition of about 1.5 mol parts. Further, when the amount added isincreased, the dielectric constant is reduced but its tendency is dull,and sinterability will be lowered at the point exceeding 5 mol parts,whereby mechanical strength (as represented by flexural strength) willbe undesirably lowered.

Accordingly, during addition of Al₂ O₃, the amount necessary forobtaining the desired dielectric constant at 5 mol parts or less can bedetermined by experiments, but addition of 0.40 to 5.00 mol parts isrequired when the ratio ε₁ /ε₂ of the dielectric constant of the firstregion ε₁ to the dielectric constant of the second region ε₂ is designedto be 10 or more.

As is apparent from Table 2, it can be understood that the dielectricconstant is changed extremely greatly by varying the amount of Al₂ O₃added.

Also from Table 2, it can be understood that the mechanical strength ofthe second region can be improved by making the amount of SiO₂ added0.05 to 2.00 mol parts per 100 mol parts of the main components of C₁.

The further addition effect of Al₂ O₃ and SiO₂ are exemplified in Table3.

In order to obtain a ceramic shown in FIG. 12, a partitioning plate wasplaced vertically at the center within the mold, and the respectivevoids separated with the partitioning plate were filled withpredetermined compositional powders shown in Table 3 and press molded,followed by preparation of dielectric porcelains according to the stepsas described below.

The starting materials of the respective samples shown in Table 1 wereweighed and pulverized and mixed in a wet system ball mill for 12 hours.After the mixture was dried, a small amount of polyvinyl alcohol wasadded as the binder and the mixture was granulated into 24 to 80 meshand molded into discs of 20 mm in diameter and 0.7 mm in thickness bymeans of a hydraulic press. Subsequently, the molded discs were calcinedin air at 950° C. for 1 hour to burn the binder. The calcined productwas cooled to room temperature and then fired in a reducing atmospherecomprising 10 vol. % of hydrogen and 90 vol. % of nitrogen at 1400° C.for 4 hours.

The semiconductor porcelain thus obtained was soaked into a suspensioncomprising a weight ratio of ethyl alcohol:Bi₂ O₃ or Na₂ O=10:1 and thenfired in an oxidizing atmosphere at 1250° C. for 0.5 hours to form aninsulating layer at the crystal grain boundary.

The flexural strength of the ceramic bonded product thus obtained wasmeasured by use of the method shown in FIG. 12. The results are shown inTable 3.

When the amount of SiO₂ added based on 100 mol parts of the maincomponents of C₁ is less than 0.05 mol parts or over 2 mol parts, noimproved effect of mechanical strength at the bonded interface with thefirst region can be recognized as shown.

Here, the particle sizes internally of the porcelain (here at thepositions of 0.1 mm, 0.3 mm from the surface) are shown in FIG. 13, whenAl₂ O₃ alone and a mixture of Al₂ O₃ and SiO₂ are respectively addedwith ethyl cellulose as the binder to be formed into a paste, which wascoated on the whole region of the both surfaces of the molded product ofC₁ with a thickness of 0.80 mm (by use of the composition of sample No.4) and subjected to thermal diffusion in the firing process forsemiconductor (1420° C., 4 hrs, N₂ /H₂ =90/10). The thickness of theporcelain was controlled to 0.63 mm, and the amounts of the mixture ofAl₂ O₃ and SiO₂ coated to 4.0-4.5 mg/cm² on front and back surfaces,respectively in each sample.

Next, a product obtained by coating the above paste on the whole regionof the surface (only one surface) K of the C₁ molded product with athickness of 0.50 mm, followed by firing as described above, wassubjected to diffusion of Bi₂ O₃ into the crystal grain boundary in airat 1250° C. for 30 minutes to insulate the grain boundary, and thenbaked with Ag electrodes of predetermined shapes, and the respectivedielectric constants were measured. The results are shown in Table 14.

As can be seen from FIG. 13 and FIG. 14, diffusion does not proceedsufficiently with Al₂ O₃ alone, and grain size and dielectric constantare markedly lowered with a mixture (and/or compound) comprising 60 to98 mol % of Al₂ O₃ and 40 to 2 mol % of SiO₂, whereby the promotioneffect of diffusion can be recognized. Thus, SiO₂ is used indispensablyin combination in the present invention as the component for promotingdiffusion of Al₂ O₃.

Here, the amount to be fed in forming a layer of the mixture comprising60 to 98 mol % of Al₂ O₃ and 40 to 2 mol % of SiO₂ on the surface of amolded product is to be described. In this case, the amount fed willvary depending on the thickness of the molded product and the amount fedis increased as the thickness is increased, but since the thickness ofthe circuit substrate employed generally frequently is at most 1.6 mm,and its relationship can be exemplified as shown in Table 4 whenconsidered within this range.

Table 4 was obtained by use of the samples prepared similarly as theceramics prepared to obtain the data in FIG. 13, except for thethickness and the firing conditions of the molded product.

From Table 4, it can be understood that the dielectric constant islowered, while the flexural strength tends to be lowered, as the amountfed of Al₂ O₃ and SiO₂ to the molded product is increased. Accordingly,it is critical that the amount fed should be determined at a level wherethe dielectric constant and the flexural strength are balanced, but atan amount of Al₂ O₃ and SiO₂ fed less than 0.3 mg/cm², the dielectricconstant becomes greater to the extent exceeding 20000, while if itexceeds 25 mg/cm², the flexural strength will be undesirably lowered togreat extent. For the above reasons, the amount fed may be suitably 0.3mg/cm² or more and 25 mg/cm² or less in practical application.

In the following, an embodiment of the steps for preparation of theceramic shown in FIGS. 6A and 6B is described by referring to FIG. 7.

(1) The starting materials for the composition of C₁ are weighed, andthen mixed in a wet system ball mill and dried.

(2) To the powder was added a binder of polyvinyl alcohol, etc., and themixture was molded into a product with a predetermined shape by pressmolding, extrusion molding, etc.

(3) Subsequently, at the predetermined portions of the surface(preferably the both confronting front and back surfaces) of the moldedproduct (shown by the symbol 51 in FIG. 6A), a paste comprising apowdery mixture of Al₂ O₃ /SiO₂ =98/2-60/40 (mol ratio) and a bindersuch as ethyl cellulose, etc. (shown by the symbol 52 in FIG. 6A) isapplied to a width of 0.5 mm.

(4) For removing the binder in the molded product and the coated paste,calcination is effected in air at 600° to 1200° C.

(5) The calcined product is fired in a reducing atmosphere of a gasmixture of hydrogen and nitrogen, a gas mixture of hydrogen and argon,etc. or in a neutral atmosphere of nitrogen, argon, etc. at 1320° to1450° C. to obtain a semiconductor porcelain. Also, during this process,Al₂ O₃ and SiO₂ coated are diffused into the inner portion.

(6) For insulating the crystal boundary of this semiconductor porcelain,the porcelain is soaked in a suspension comprising a weight ratio ofethyl alcohol:Bi₂ O₃ or Na₂ O=10:1, followed by firing in air at 1100°to 1300° C.

(7) Ag electrode (shown by the symbol 50 in FIG. 6B) was baked at theregion corresponding to the necessary functional element portion.

The electrode is not limited to Ag, but Au, Al, Ni, Cu, Zn, etc. may bealso available.

In FIG. 6B, products with a=3 mm, b=1, mm, c=3 mm, d=10 mm, e=0.55 mm,and e=1.6 mm (a-d are the same) were prepared.

The capacitance of the functional portion as the capacitor of thecircuit substrate thus prepared and the capacitance exhibiting itsseparated state are shown in Table 5.

The capacitance of the functional portion as the capacitor was measuredas the capacitance between the electrodes with the dielectric porcelainsubstrate being sandwiched in parallel in its thickness direction, andthe capacitance exhibiting its separated state was shown as thecross-capacitance with the capacitance between the electrodes on thesame plane.

As described above, if a layer comprising a mixture of Al₂ O₃ and SiO₂can be formed at a predetermined portion on the surface of the moldedproduct of C₁ and diffused into the molded product, a region differinggreatly in dielectric constant (the second region) can be formed easilyin the steps.

The above molded product to be used in the present invention isgenerally a molded product (pressed powder or calcined product of saidpressed powder, etc.) which is the precursor for forming the porcelain,but a molded product already formed into a porcelain, or a moldedproduct by pulverizing porcelain and molding it again into pressedpowder may be also used.

In the present invention, diffusion of Al₂ O₃ and SiO₂ is generallyperformed by thermal diffusion by way of firing. Therefore, by use of amolded product which is the precursor for forming the above porcelain,thermal diffusion by firing and formation into porcelain can be effectedat the same time as extremely advantageous in industry.

The present invention utilizes the property that the electriccharacteristics of the porcelain can be changed to great extent byaddition of minute amounts of Al₂ O₃ and SiO₂, whereby separation of thefunctional portions within a ceramic is rendered possible.

More specifically, by permitting Al₂ O₃ and SiO₂ to exist internally ofthe porcelain by diffusion, etc., for example, dielectric constant willbe changed remarkably. Therefore, regions with different dielectricconstants can be sectionalized without changing greatly the compositionof the porcelain to be built within the same ceramic.

Formation of Al₂ O₃, SiO₂ layer on the porcelain surface can beperformed by, for example, printing, spraying, chemical vapordeposition, evaporation, dipping, etc.

According to the ceramic of the present invention, a plurality offunctional portions can be built in under the state sufficientlyseparated from each other.

Also, according to the circuit substrate and the electronic circuitsubstrate of the present invention, by being constituted of a ceramiccapable of having a plurality of functional portions built therein assectionalized under the state sufficiently separated from each other asdescribed above, a plurality of electronic part constituent units can bebuilt in under the state sufficiently separated mutually as the devicefunctional portions from each other.

                                      TABLE 1                                     __________________________________________________________________________                 Contents of                                                                            Additive        Temperature                                          other components                                                                       for             change rate of                              Composition of                                                                         (mol parts per                                                                         formation       dielectric                                  main components                                                                        100 mol parts of                                                                       of              constant                                Sample                                                                            (mol %)  main components)                                                                       insulating                                                                             tanδ                                                                       IR  (%, based on 25° C.)             No. TiO.sub.2                                                                          SrO MnO.sub.2                                                                          Y.sub.2 O.sub.3                                                                   layer                                                                              ε                                                                         (%)                                                                              (MΩ)                                                                        -25° C.                                                                     +85° C.                     __________________________________________________________________________     1* 49.20                                                                              50.80                                                                             3.50 0.12                                                                              Bi.sub.2 O.sub.3                                                                    22000                                                                            0.9                                                                              7100                                                                              13.8 -12.7                               2  49.70                                                                              50.30                                                                             3.50 0.12                                                                              ↑                                                                             47000                                                                            0.8                                                                              5600                                                                              12.1 -10.3                               3  50.20                                                                              49.80                                                                             3.50 0.12                                                                              ↑                                                                            119000                                                                            0.7                                                                              4700                                                                              9.7  -10.0                               4  51.00                                                                              49.00                                                                             3.50 0.12                                                                              ↑                                                                            132000                                                                            0.7                                                                              4300                                                                              8.2  -6.8                                5  53.40                                                                              46.60                                                                             3.50 0.12                                                                              ↑                                                                            101000                                                                            0.8                                                                              3900                                                                              9.1  -7.9                                6  53.60                                                                              46.40                                                                             3.50 0.12                                                                              ↑                                                                             89000                                                                            1.3                                                                              3100                                                                              10.2 -9.8                                7* 54.20                                                                              45.80                                                                             3.50 0.12                                                                              ↑                                                                             20000                                                                            2.3                                                                              1500                                                                              10.0 -9.5                                8* 51.00                                                                              49.00                                                                             0.30 0.12                                                                              ↑                                                                             31000                                                                            0.7                                                                              9600                                                                              14.1 -13.2                               9  51.00                                                                              49.00                                                                             0.70 0.12                                                                              ↑                                                                             40000                                                                            0.7                                                                              8200                                                                              13.6 -13.0                              10  51.00                                                                              49.00                                                                             2.10 0.12                                                                              ↑                                                                            118000                                                                            0.6                                                                              4100                                                                              8.1  -7.8                               11  51.00                                                                              49.00                                                                             3.00 0.12                                                                              ↑                                                                            134000                                                                            0.5                                                                              3900                                                                              7.5  -7.3                               12  51.00                                                                              49.00                                                                             4.80 0.12                                                                              ↑                                                                            111000                                                                            0.8                                                                              4200                                                                              8.2  -8.1                               13  51.00                                                                              49.00                                                                             5.10 0.12                                                                              Bi.sub.2 O.sub.3                                                                    92000                                                                            1.9                                                                              4300                                                                              8.5  -7.8                                14*                                                                              51.00                                                                              49.00                                                                             5.50 0.12                                                                              ↑                                                                             67000                                                                            3.2                                                                              4500                                                                              8.4  -8.5                                15*                                                                              51.00                                                                              49.00                                                                             3.50 0.01                                                                              ↑                                                                             21000                                                                            0.5                                                                              9600                                                                              8.0  -8.6                               16  51.00                                                                              49.00                                                                             3.50 0.03                                                                              ↑                                                                             62000                                                                            0.5                                                                              8300                                                                              7.9  -8.2                               17  51.00                                                                              49.00                                                                             3.50 0.06                                                                              ↑                                                                            106000                                                                            0.6                                                                              6700                                                                              7.6  -8.3                               18  51.00                                                                              49.00                                                                             3.50 0.20                                                                              ↑                                                                            115000                                                                            0.8                                                                              3500                                                                              6.9  -7.4                               19  51.00                                                                              49.00                                                                             3.50 0.27                                                                              ↑                                                                            108000                                                                            0.9                                                                              3200                                                                              7.8  -8.0                               20  51.00                                                                              49.00                                                                             3.50 0.37                                                                              ↑                                                                             67000                                                                            1.9                                                                              1700                                                                              7.8  -7.5                                21*                                                                              51.00                                                                              49.00                                                                             3.50 0.42                                                                              ↑                                                                             48000                                                                            2.8                                                                              1100                                                                              7.9  -8.1                               22  51.00                                                                              49.00                                                                             2.10 0.12                                                                              Na.sub.2 O                                                                         140000                                                                            0.6                                                                              3900                                                                              7.4  -6.3                               23  51.00                                                                              49.00                                                                             3.00 0.12                                                                              ↑                                                                            144000                                                                            0.7                                                                              3500                                                                              6.8  -8.2                               24  51.00                                                                              49.00                                                                             4.80 0.12                                                                              ↑                                                                            128000                                                                            0.8                                                                              3400                                                                              7.4  -8.1                               __________________________________________________________________________     *outside the range of the present invention                              

                                      TABLE 2                                     __________________________________________________________________________                                                       Volume                                                 Additive          Average                                                                            resistivity                                            for               particle                                                                           of                             Components of                                                                          Contents of other components                                                                 formation         diameter                                                                           semiconduc-                    main components                                                                        (mol parts per 100 mol parts                                                                 of                of   tor-   Flexural            Sample                                                                            (mol %)  of main components)                                                                          insulat-   tan δ                                                                      IR  porcelain                                                                          porcelain                                                                            strength            No. TiO.sub.2                                                                         SrO  MnO.sub.2                                                                         Y.sub.2 O.sub.3                                                                  SiO.sub.2                                                                         Al.sub.2 O.sub.3                                                                  ing layer                                                                          ε                                                                           (%)                                                                              (MΩ)                                                                        (μ)                                                                             (cm)   (kg/cm.sup.2)       __________________________________________________________________________     4  51.00                                                                             49.00                                                                              3.50                                                                              0.12                                                                             --  --  Bi.sub.2 O.sub.3                                                                   132000                                                                              0.7                                                                              4300                                                                              64   3 × 10.sup.1                                                                   1500                25  "   "    "   "  --  0.2 "    86000 0.7                                                                              4800                                                                              46   4 × 10.sup.2                                                                   1600                26  "   "    "   "  --  0.5 "    11000 0.9                                                                              6700                                                                              30   3 × 10.sup.4                                                                   1700                27  "   "    "   "  --  1.5 "    430   1.2                                                                              8600                                                                              14   8 × 10.sup.5                                                                   1900                28  "   "    "   "  --  4.5 "    330   1.4                                                                              9100                                                                               6   2 × 10.sup.6                                                                   1700                29  "   "    "   "  --  5.5 "    310   1.8                                                                              9300                                                                               4   5 × 10.sup.6                                                                   1100                30  "   "    "   "   0.03                                                                             1.5 "    420   1.2                                                                              8800                                                                              14   8 × 10.sup.5                                                                   1900                31  "   "    "   "   0.06                                                                             "   "    400   1.2                                                                              9000                                                                              12   9 × 10.sup.5                                                                   2100                32  "   "    "   "  0.8 "   "    370   1.0                                                                              9400                                                                              10   1 × 10.sup.6                                                                   2300                33  "   "    "   "  1.8 "   "    350   1.0                                                                              9700                                                                              10   2 × 10.sup.6                                                                   2000                34  "   "    "   "  2.2 "   "    350   0.9                                                                              9800                                                                               9   3 × 10.sup.6                                                                   1300                35  "   "    "   "  0.8 0.5 "    10000 0.9                                                                              7200                                                                              26   4 × 10.sup.4                                                                   2200                36  "   "    "   "  0.8 4.5 "    310   1.3                                                                              9600                                                                               5   4 × 10.sup.6                                                                   2100                __________________________________________________________________________

                  TABLE 3                                                         ______________________________________                                                                      Flexural strength                               Sample                                                                              Composition Composition of bonded                                       No.   of portion 121                                                                            of portion 122                                                                            product                                         ______________________________________                                        37    Sample No. 4                                                                              Sample No. 4                                                                              1500                                            38    "           Sample No. 25                                                                             1300                                            39    "           Sample No. 26                                                                             1100                                            40    "           Sample No. 27                                                                             1000                                            41    "           Sample No. 28                                                                             1000                                            42    "           Sample No. 29                                                                              780                                            43    "           Sample No. 30                                                                             1200                                            44    "           Sample No. 31                                                                             1500                                            45    "           Sample No. 32                                                                             1700                                            46    "           Sample No. 33                                                                             1600                                            47    "           Sample No. 34                                                                              970                                            48    "           Sample No. 35                                                                             1600                                            49    "           Sample No. 36                                                                             1500                                            ______________________________________                                    

                                      TABLE 4                                     __________________________________________________________________________        Molding    Amount fed                  Flexural                           Sample                                                                            thickness                                                                          Al.sub.2 O.sub.3 /SiO.sub.2                                                         to molding                                                                          Firing (diffusion) condition                                                                  Dielectric                                                                          strength                           No. (mm) (mol ratio)                                                                         (mg/cm.sup.2)                                                                       Temperature (°C.)                                                                Time (Hr)                                                                           constant                                                                            (Kg/cm.sup.2)                      __________________________________________________________________________     50*                                                                              2.0  --    0     1435      6     134000                                                                              1700                                51*                                                                              "    80/20 0.15  "         "     85000 1700                               52  "    "     0.4   "         "     5100  1600                               53  "    "     1.5   "         "     1500  1600                               54  "    "     8.0   "         "     750   1400                               55  "    "     22    "         "     640   1100                                56*                                                                              "    "     29    "         "     610    680                                57*                                                                              "    99/1  8.0   "         "     33000 1700                               58  "    98/2  8.0   "         "     6700  1600                               59  "    95/5  8.0   "         "     2100  1500                               60  "    60/40 8.0   "         "     1600  1600                                61*                                                                              "    55/45 8.0   "         "     19000 1600                                62*                                                                              0.7  --    0     1420      4     130000                                                                              1700                                63*                                                                              "    80/20 0.15  "         "     21000 1700                               64  "    "     0.4   "         "     2300  1600                               65  "    "     1.5   "         "     670   1500                               66  "    "     8.0   "         "     490   1200                               67  "    "     22    "         "     480    960                                68*                                                                              "    "     29    "         "     490    520                               __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________                                       Porcelain                                                                          Functional                                                                            Separating                                     Functional device separating portion                                                            plate                                                                              device portion                                                                        portion cross-                Sample                                                                            Composition of functional                                                                  Al.sub.2 O.sub.3 /SiO.sub.2                                                         Amount fed to molding                                                                     thickness                                                                          capacitance                                                                           capacitance                   No. device portion                                                                             (mol ratio)                                                                         (mg/cm.sup.2)                                                                             (mm) (nF)    (pF)                          __________________________________________________________________________     69*                                                                              the same as Sample No. 4                                                                   80/   0.15        0.55 62      3300                          70  "            "     0.4         "    60      380                           71  "            "     1.5         "    59       95                           72  "            "     8.0         "    57       81                           73  "            "     22          "    54       78                            74*                                                                              "            "     29          "    41       79                            75*                                                                              "            99/1  8.0         1.6  21      9400                          76  "            98/2  "           "    20      960                           77  "            95/5  "           "    20      350                           78  "            80/20 "           "    17      140                           79  "            60/40 "           "    19      230                            80*                                                                              "            55/45 "           "    18      5200                          __________________________________________________________________________     *is outside scope of the invention                                       

What is claimed is:
 1. A ceramic comprising therein at least twodielectric regions including (a) a first region having (i) a principalcomposition consisting of from 49.50-54.00 mole percent of TiO₂ and from50.50-46.00 mole percent of SrO; (ii) from 0.50-5.30 moles MnO₂ per 100moles of the principal composition and (iii) from 0.02-0.40 moles Y₂ O₃per 100 moles of said principal composition; and (b) a second regionhaving (i) a principal composition consisting of from 49.50-54.00 molepercent of TiO₂ and from 50.50-46.00 mole percent of SrO; (ii) from0.50-5.30 moles MnO₂ per 100 moles of the principal composition; (iii)from 0.02-0.40 moles Y₂ O₃ per 100 moles of said principal composition;and (iv) from 0.40-5.00 moles Al₂ O₃ and from 0.05-2.00 moles SiO₂ per100 moles of said principal composition.
 2. A ceramic according to claim1 wherein the first region has a dielectric constant which is at least10 times the dielectric constant of the dielectric constant of thesecond region.
 3. The ceramic according to claim 1 further including atleast one oxide for insulating the crystal grain boundary, said oxideselected from the group consisting of iron oxide, cobalt oxide, vanadiumoxide, chromium oxide, lead oxide, copper oxide, bismuth oxide, andsodium oxide.
 4. A circuit substrate comprising:a ceramic comprisingtherein at least two dielectric regions including (a) a first regionhaving (i) a principal composition consisting of from 49.50-54.00 molepercent of TiO₂ and from 50.50-46.00 mole percent of SrO; (ii) from0.50-5.30 moles MnO₂ per 100 moles of the principal composition and(iii) from 0.02-0.40 moles Y₂ O₃ per 100 moles of said principalcomposition; and (b) a second region having (i) a principal compositionconsisting of from 49.50-54.00 mole percent of TiO₂ and from 50.50-46.00mole percent of SrO; (ii) from 0.50-5.30 moles MnO₂ per 100 moles of theprincipal composition; (iii) from 0.02-0.40 moles Y₂ O₃ per 100 moles ofsaid principal composition; and (iv) from 0.40-5.00 moles Al₂ O₃ andfrom 0.05-2.00 moles SiO₂ per 100 moles of said principal compositionand electrodes internally of or at the surface of said ceramic.
 5. Thecircuit substrate according to claim 4 wherein the first region has adielectric constant which is at least 10 times the dielectric constantof the dielectric constant of the second region.
 6. The circuitsubstrate according to claim 4 further including at least one oxide forinsulating the crystal grain boundary, said oxide selected from thegroup consisting of iron oxide, cobalt oxide, vanadium oxide, chromiumoxide, lead oxide, copper oxide, bismuth oxide, and sodium oxide.